One problem that has plagued machinists for years is the drag line which is frequently left on a machined surface when the tool is returned after completion of a machining operation. This line, which is sometimes also referred to as a draw line or a witness line, is caused by the fact that when the tool is traversing the workpiece surface during machining the entire machine is under substantial stress, and upon completion of the machining operation the suddenly unstressed components of the machine assume a slightly different position in which there may be slight interference between the tool and the just-machined surface, whereupon when the tool is returned by reversing the feed it leaves a shallow spiral across this surface. Drag lines are also caused due to the fact that most machined surfaces are not totally flat but comprise a series of small ridges and valleys, and withdrawal of the tool, without also moving it away from the workpiece, causes it to intersect these ridges with the result that the just-machined surface again may have a noticeable shallow spiral formed thereon. This type of problem is encountered in numerous machining operations, including boring, facing and turning operations.
One way to avoid drag line formation is to move the tool away from the machined surface upon completion of the machining operation and prior to returning it, however this adds an undesirable step to the machining sequence. Other techniques have evolved for eliminating this problem but most of them have one disadvantage or another. For example, some are not applicable to boring, turning and facing on a universal basis, some do not permit a live return of the spindle in the case of a boring operation, some do not permit boring against a shoulder without leaving a drag line or chatter marks on the shoulder, some require manual actuation by an external power source, some do not permit the use of multiple tools in a single operation, and like disadvantages.
It is therefore a primary object of the present invention to provide an improved an improved tool holding assembly which is relatively simple and inexpensive in construction and which overcomes most if not all of the aforesaid disadvantages of prior art devices for avoiding drag lines. More specifically, objects of the present invention reside in the provision of such an assembly which permits live return of the spindle at normal operating speeds when performing boring operations on a boring machine, which permits boring, facing and turning operations, which permits boring against shoulders without a dwell at the end of the feed and without chattering, which is fully self-actuated by engagement with the workpiece and self-retracting to an inactive position by virtue of internal spring means, which permits withdrawal or return of the tool during a machining operation for measuring and then continuance of the machining operation with minimal evidence of interruption on the machined surface, within normal machining parameters, which permits the use of multiple tools in a single machining operation because the self-retracting means are a part of each individual tool, and like advantages; all without forming a drag line on the machined surface, even if it includes a shoulder, and without moving the tool away from the machined surface prior to return.
A further object of the present invention resides in the provision of a structure of the aforedescribed type which is so designed that it is not subject to malfunction due to the lodging of machined chips or like foreign matter within the working parts thereof, thus insuring reliability even in the most adverse environments.
These and other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.